Process for casting a metal

ABSTRACT

This invention relates to an improved process for casting a metal by pouring molten metal into and around a mold assembly, where a riser is a component of the mold assembly. The process comprises (a) inserting a riser insert into the cavity of the riser, and (b) then allowing molten metal to flow into the cavity of the riser containing the riser insert. The process is carried out in a manner such that the density and the shape of the riser insert enables the riser insert to float on the surface of the molten metal when the molten metal enters the cavity of the riser.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable.

CLAIM TO PRIORITY

[0002] Not Applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0003] Not Applicable.

REFERENCE TO A MICROFICHE APPENDIX

[0004] Not Applicable.

BACKGROUND OF THE INVENTION

[0005] (1) Field of the Invention

[0006] This invention relates to an improved process for casting a metalby pouring molten metal into and around a casting assembly, where ariser is a component of the casting assembly. The process comprises (a)inserting a riser insert into the cavity of the riser, and (b) thenallowing molten metal to flow into the cavity of the riser containingthe riser insert. The density of the riser insert is such that the riserinsert floats above the surface of the molten metal when the moltenmetal enters the cavity of the riser and provides a thermal barrier toreduce heat loss from the riser.

[0007] (2) Description of the Related Art

[0008] A casting assembly typically consists of a pouring cup, a gatingsystem (including downsprues, choke, and runner), risers, molds, cores,and other components. To produce a metal casting, metal is poured intothe pouring cup of the casting assembly and passes through the gatingsystem to the mold and/or core assembly where it cools and solidifies.

[0009] The metal part is then removed by separating it from the coreand/or mold assembly.

[0010] The molds and/or cores used in the casting assembly are typicallymade of sand and a binder, often by the no-bake or cold-box process. Thesand is mixed with a chemical binder and typically cured in the presenceof a liquid or vaporous catalyst after it is shaped.

[0011] Risers are cavities in which excess molten metal flows. Theexcess molten metal is needed to compensate for contractions orshrinkage of metal, which occur during the casting process. Metal fromthe riser fills such voids created in the casting when metal from thecasting contracts. The metal from the riser must remain in a liquidstate for a longer period of time, so it can provide molten metal to thecasting as it cools and solidifies. Thus, it is advantageous to keep themolten metal in the riser hot as long as possible.

[0012] Heat loss from the riser occurs by convection to the coolersurroundings and through radiation to the cooler atmosphere. Because ofthis problem with heat loss associated with open risers, closed risers,which are surrounded by and covered with sleeve material are sometimesused instead of open risers. One problem associated with the use ofclosed risers is that the operator cannot see when the riser cavity isfull by visual inspections. In addition, closed risers do not provideventing of mold gasses to the atmosphere during pouring. Theseconditions can result in over-filling of the mold, metal spillage, andresulting safety hazards.

[0013] Because of the problems associated with using closed risers, openrisers are sometimes preferred. When an open riser is used, the operatorcan visually inspect the riser cavity and determine when the level ofmolten metal in the riser cavity is appropriate. After the appropriatelevel is reached, in order to prevent heat loss from an open riser, thetop of the riser cavity is covered with a hot-topping, e.g. a granularmaterial, a powder, rice hulls, a blanket (see U.S. Pat. No. 3,876,420),and solid covers (graphite) having an insulating properties, exothermicproperties, or both, within a relatively short period of time to preventexcessive heat loss. When an open riser is used, typically an extraperson is needed to inspect the riser cavity and apply the toppingfollowing pouring.

[0014] If the hot-topping is a granular or powder material, it oftenspills across the top of the casting assembly onto the floor of thefoundry. Because there is often spillage or misapplication, it is normalpractice to apply much more than the optimum amount that is necessary.Additionally, when powdered materials are used, the powdered materialscan miss the top of the riser and spill onto the casting assembly whereit can eventually get mixed into the molding sand and consequently causecasting defects.

[0015] If blankets are placed on top of the riser, before the riser isfilled with metal, the metal pourer is not able to see the metal fillthe riser and the molten metal could overflow and spill onto the floor.If blankets are placed on the riser after the appropriate level ofmolten metal is reached, an extra person is usually required to inspectthe riser cavity and to place the blanket on top of the open riser whilethe metal pourer moves on to pour the next mold. Furthermore, the metalin the riser is open to the atmosphere during the time between fillingand when the blanket is applied, which results in heat loss. The longerthe delay before the cover is placed over the cavity, the more heat islost and the effectiveness of the riser is reduced.

[0016] All citations referred to under this description of the “RelatedArt” and in the “Detailed Description of the Invention” are expresslyincorporated by reference.

BRIEF SUMMARY OF THE INVENTION

[0017] This invention relates to an improved process for casting a metalby pouring molten metal into and around a mold assembly, where a riseris a component of the mold assembly. The process comprises (a) insertinga riser insert into the cavity of the riser, and (b) then allowingmolten metal to flow into the cavity of the riser containing the riserinsert. The process is carried out in a manner such that the density andthe shape of the riser insert enables the riser insert to float on thesurface of the molten metal when the molten metal enters the cavity ofthe riser. When the molten metal enters the riser cavity, the shapedmaterial floats on top of the molten metal and, thereby, prevents theheat of the molten metal from escaping.

[0018] The riser insert is slightly smaller than the internal crosssection of the riser, so the riser 11 insert can be easily dropped orinserted into the riser. In order to prevent the riser insert fromfalling through the riser cavity into other parts of the castingassembly, the bottom of the riser is shaped as a breaker core or theneckdown portion of a neckdown riser. Alternatively, a barrier, e.g. anail, rod, foam filler, filter cloth, or fin, is inserted into the risercavity below the riser insert, which prevents the riser insert fromfalling into other parts of the casting assembly.

[0019] There are many advantages to the subject process. Certainly, oneof the major advantages is that the loss of heat is minimized from thetime the pour begins, because the riser insert is present before thepouring begins. Furthermore, the metal pourer can see the riser insertrising, so he knows when the riser is filled and, thus, avoids overfilling the mold. Because the riser insert can be placed in the riserbefore the metal is poured, extra manpower is not needed to cover theriser cavity when the riser cavity is filled with molten metal.Additionally, because the riser insert is in the riser while the castingassembly is setting before the molten metal is poured, it prevents dirtfrom falling through the riser cavity into the casting assembly. Thisproblem is of particular concern when casting larger parts, where thepour is delayed for several hours or even days after the castingassembly is arranged. If dirt gets into the mold, it must be removed, orcasting defects are likely to result. The removal of dirt involves extratime and money. The riser insert can be properly sized to provide theoptimum insulating and/or exothermic properties without the use ofexcessive material and without the under application of materials andexcessive heat loss.

[0020]FIGS. 9 and 10 illustrate further advantages of this invention.FIGS. 9 and 10 show the performance of a riser which is covered bytraditional hot topping material (FIG. 9) compared to using a floatingriser insert (FIG. 10). The floating riser insert keeps the top of theriser liquid longer and prevents the formation of the layer ofsolidified metal skin that forms on the top of the riser when a hottopping material is used.

[0021] The formation of a skin on top of a riser can prevent theatmospheric pressure from getting inside the riser so it can push on theremaining liquid metal. This is why the design of blind risersincorporates a “firecracker” (Williams) core that creates a hot spot atthe top of the riser. This helps keep the top open and allows theatmospheric pressure to push the liquid metal into the shrinking castingcavity. Test results indicate that the floating riser insert may also beused in a blind riser application and could eliminate the need for thefirecracker core.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0022]FIG. 1 Is a copy of a photograph showing the top of a mold with anopen riser before the riser insert is added.

[0023]FIG. 2 Is a copy of a photograph showing the top of a mold where ariser insert was placed into the open riser and settled in a verticalposition.

[0024]FIG. 3 Is a copy of a photograph showing the top of a mold where ariser insert was placed into the open riser and settled in a horizontalposition.

[0025]FIG. 4 Is a copy of a photograph showing the pouring of metal intothe mold which contained the vertical positioned insert and the insertfloating on top of the raising metal in the riser.

[0026]FIG. 5 Is a copy of a photograph showing the top of a mold withthe insert covering the top of the open riser after the metal waspoured.

[0027]FIG. 6 Is a copy of a photograph showing the pouring of metal intothe mold which contained the horizontal positioned insert and the insertfloating on top of the raising metal in the riser.

[0028]FIG. 7 Is a copy of a photograph showing the top of a mold wherean exothermic insert was used and the exothermic insert igniting afterthe filling of the mold.

[0029]FIG. 8 Is a copy of a photograph showing the top of the moldsafter the metal was poured.

[0030]FIG. 9 Is a copy of a photograph showing a cross-section of ariser where a traditional exothermic hot topping was used to cover thetop of the riser after the mold was poured.

[0031]FIG. 10 Is a copy of a photograph showing a cross-section of ariser where an exothermic floating riser insert was used in place of hoptopping to cover the top of the riser before the mold was poured.

DETAILED DESCRIPTION OF THE INVENTION

[0032] The detailed description and examples will illustrate specificembodiments of the invention and will enable one skilled in the art topractice the invention, including the best mode. It is contemplated thatmany equivalent embodiments of the invention will be operable besidesthese specifically disclosed.

[0033] For purposes of describing this invention, a “riser insert” is ashape, typically a circular disk, which fits into a riser cavity andwill float on top of the molten metal when it enters the riser cavity.The riser is shaped so that the riser insert will not fall through theriser into other parts of the casting assembly, or the riser contains abarrier that prevents the riser insert from falling through the risercavity to other parts of the casting assembly.

[0034] When the metal is poured and fills the riser, the riser insertfloats on top of the molten metal. To float, the riser insert must bemade of a material that has a density lower than that of the metal beingpoured. The riser insert can be made from a variety of materials, e.g.ceramic fiber-based refractories, granular refractories, sand,microsphere refractories, paper, cardboard, etc. It is possible to usematerials that bum when exposed to the heat of the molten metal,provided the material stays in place while the metal cools to preventthe loss of heat from the riser. It is even possible to use paper orcardboard if treated with fire retardant materials, so the paper burnsslower. The ashes that are left create an insulating barrier between thetop of the riser and the air above the mold.

[0035] The riser insert is preferably used with an open riser (one thathas a top that is open to the atmosphere), preferably an open riser thathas a breaker core on the bottom or is a neckdown type riser where thebottom of the riser where it contacts the casting is smaller than theupper section of the riser. These types of risers will naturally keepthe riser insert from falling down into the casting cavity.

[0036] In practice the riser insert is typically placed in the risercavity when the mold is assembled. This eliminates the need for a personat the pouring area to place toppings or blankets on the molds afterthey are poured.

[0037] Insulating or exothermic hot-topping is typically applied on topof the liquid metal in the riser after the mold has been poured. Theapplication of the hot-topping needs to occur within a relatively shortperiod of time to prevent excessive heat loss. This typically dictatesthat a second person is needed to follow the pourer to apply thetopping. The hot-topping material is typically a granular or powdermaterial that is applied by volume and may or may not be measured. Thematerial often spills across the top of the mold or on the floor. Toallow for spillage or misapplication, it is normal practice to applymuch more than the optimum amount.

[0038] Preferably used to make the riser inserts are low densitymicrospheres. Riser inserts made with low-density microspheres aredimensional accurate and maintain their dimensional accuracy when themolten metal is poured into and around the casting assembly. This isimportant because the dimensionally accurate riser inserts do not stickin the riser cavity, and, consequently, are free floating. Riser insertsmade from these materials have thermal conductivities about ¼ thethermal conductivities of corresponding riser inserts made from sand andthey provide better insulating characteristics. Furthermore, becausethey are light-weight and have a low-density, they are easy to handleand provide the maximum buoyant force to insure that the riser insertfloats to the top of the riser cavity when the molten metal is poured.

[0039] Examples of microspheres include hollow aluminosilicatemicrospheres, including aluminosilicate zeospheres. The riser insertsmade with aluminosilicate hollow microspheres have low densities, lowthermal conductivities, and excellent insulating properties. The thermalconductivity of the hollow aluminosilicate microspheres ranges fromabout 0.1 W/m.K to about 0.6 W/m.K at room temperature, more typicallyfrom about 0.15 W/m.K to about 0.4 W/m.K.

[0040] The hollow aluminosilicate microspheres used to make the riserinserts typically have a particle size of about 10 to 350 microns withvarying wall thickness. Preferred are hollow aluminosilicatemicrospheres having an average diameter greater than 150 microns and awall thickness of approximately 10% of the particle size. It is believedthat hollow microspheres made of material other than aluminosilicate,having insulating properties, can also be used to replace or used incombination with the hollow aluminosilicate microspheres.

[0041] The weight percent of alumina to silica (as SiO₂) in the hollowaluminosilicate microspheres can vary over wide ranges depending on theapplication, for instance from 25:75 to 75:25, typically 33:67 to 50:50,where said weight percent is based upon the total weight of the hollowmicrospheres. It is known that hollow aluminosilicate microsphereshaving a higher alumina content are better for making larger riserinserts used in pouring metals such as iron and steel which have castingtemperatures of 1300° C. to 1700° C., because hollow aluminosilicatemicrospheres having more alumina have higher melting points. Thus riserinserts made with these hollow aluminosilicate microspheres will notdegrade as easily at higher temperatures. The density of the riserinsert typically ranges from about 0.3 g/cc to about 1.6 g/cc, moretypically from about 0.4 g/cc to about 0.6 g/cc.

[0042] In some cases, it is desirable to have a riser insert havingexothermic properties, in order to supply additional heat to the moltenmetal in the riser cavity. Riser inserts are rendered exothermic by theaddition of an oxidizable metal and an oxidizing agent to theformulation used to make the riser insert. The oxidizing agent iscapable of generating an exothermic reaction when it comes into contactwith the molten metal poured. The oxidizable metal typically isaluminum, although magnesium and similar metals can also be used.

[0043] When aluminum metal is used as the oxidizable metal for theexothermic riser insert, it is typically used in the form of aluminumpowder and/or aluminum granules. The oxidizing agents used for theexothermic riser insert includes iron oxide, manganese oxide, etc.Oxides do not need to be present at stoichiometric levels to satisfy themetal aluminum fuel component since the riser inserts and molds in whichthey are contained are permeable. Thus oxygen from the oxidizing agentsis supplemented by atmospheric oxygen when the aluminum fuel is burned.Typically the weight ratio of aluminum to oxidizing agent is from about10:1 to about 2:1, preferably about 5:1 to about 2.5:1.

[0044] The thermal properties of the exothermic riser insert areenhanced by the heat generated, which reduces the temperature loss ofthe molten metal in the riser, thereby keeping it hotter and liquidlonger. The typical exotherm in sleeves and sleeve related productsresults from the oxidizing reaction of aluminum metal. A mold and/orcore typically does not exhibit exothermic properties.

[0045] In addition, the riser insert formulation may contain differentfillers and additives, such as cryolite (Na₃AlF₆), potassium aluminumtetrafluoride, potassium aluminum hexafluoride, nitrates, paper, woodflour, sand, etc.

[0046] The binders that are used to hold the riser insert compositiontogether are well known in the foundry art. Any no-bake, cold-boxbinder, oil sand, or shell resin, which will sufficiently hold the riserinsert composition together in the shape of a riser insert andpolymerize in the presence of a curing catalyst, will work. Examples ofsuch binders are phenolic resins, phenolic urethane binders, furanbinders, alkaline phenolic resole binders, acid curable shell resinsbased upon phenolic novolac resins, and epoxy-acrylic binders amongothers. Particularly preferred are epoxy-acrylic binders (e.g. ISOSET®binders sold by Ashland Specialty Chemical, a division of Ashland Inc.),epoxy-acrylic-isocyanate binders e.g. ISOMAX® binders sold by AshlandSpecialty Chemical, a division of Ashland Inc.), and phenolic urethanebinders (e.g. EXACTCAST™ and ISOCURE® binders sold by Ashland SpecialtyChemical, a division of Ashland Inc.) cold-box binders. The phenolicurethane binders are described in U.S. Pat. Nos. 3,485,497 and3,409,579, which are hereby incorporated into this disclosure byreference. These binders are based on a two part system, one part beinga phenolic resin component and the other part being a polyisocyanatecomponent. The epoxy-acrylic binders, cured with sulfur dioxide in thepresence of an oxidizing agent, are described in U.S. Pat. No.4,526,219, which is hereby incorporated into this disclosure byreference. The epoxy-acrylic-isocyanate binders, cured with a volatileamine, are described in U.S. Pat. No. 5,688,837, which is herebyincorporated into this disclosure by reference.

[0047] The amount of binder needed is an effective amount to maintainthe shape of the riser insert and allow for effective curing, i.e. whichwill produce a riser insert which can be handled or self-supported aftercuring. An effective amount of binder will vary greatly depending uponthe materials used to make the insert and can range from 0.8% to 14%based on the weight of the insert composition. Preferably the amount ofbinder ranges from about 1 weight percent to about 12 weight percent.

[0048] Curing the riser insert by the no-bake process takes place bymixing a liquid curing catalyst with the riser insert mix (alternativelyby mixing the liquid curing catalyst with the riser insert compositionfirst), shaping the riser insert mix containing the catalyst, andallowing the riser insert shape to cure, typically at ambienttemperature without the addition of heat. The preferred liquid curingcatalyst is a tertiary amine and the preferred no-bake curing process isdescribed in U.S. Pat. No. 3,485,797, which is hereby incorporated byreference into this disclosure. Specific examples of such liquid curingcatalysts include 4-alkyl pyridines wherein the alkyl group has from oneto four carbon atoms, isoquinoline, arylpyridines such as phenylpyridine, pyridine, acridine, 2-methoxypyridine, pyridazine, 3-chloropyridine, quinoline, N-methyl imidazole, N-ethyl imidazole,4,4′-dipyridine, 4-phenylpropylpyridine, 1-methylbenzimidazole, and1,4-thiazine.

[0049] Curing the riser insert by the cold-box process takes place byblowing or ramming the riser insert mix into a pattern and contactingthe riser insert with a vaporous or gaseous catalyst. Various vapor orvapor/gas mixtures or gases such as tertiary amines, carbon dioxide,methyl format, and sulfur dioxide can be used depending on the chemicalbinder chosen. Those skilled in the art will know which gaseous curingagent is appropriate for the binder used. For example, an aminevapor/gas mixture is used with phenolic-urethane resins. Sulfur dioxide(in conjunction with an oxidizing agent) is used with an epoxy-acrylicresins. See U.S. Pat. No. 4,526,219, which is hereby incorporated, intothis disclosure by reference. Carbon dioxide (see U.S. Pat. No.4,985,489, which is hereby incorporated into this disclosure by,reference) or methyl esters (see U.S. Pat. No. 4,750,716 which is herebyincorporated into this disclosure by reference) are used with alkalinephenolic resole resins. Carbon dioxide is also used with binders basedon silicates. See U.S. Pat. No. 4,391,642, which is hereby incorporated,into this disclosure by reference.

[0050] Preferably the binder is an ISOCURE® cold-box phenolic urethanebinder cured by passing a tertiary amine gas, such as triethylamine,through the molded riser insert mix in the manner as described in U.S.Pat. No. 3,409,579, or the epoxy-acrylic binder cured with sulfurdioxide in the presence of an oxidizing agent as described in U.S. Pat.No. 4,526,219. Typical gassing times are from 0.5 to 3.0 seconds,preferably from 0.5 to 2.0 seconds. Purge times are from 1.0 to 60seconds, preferably from 1.0 to 10 seconds.

Abbreviations

[0051] The following abbreviations are used:

[0052] Casting assembly—assembly of casting components such as pouringcup, downsprue, gating system (downsprue, runner, choke), molds, cores,risers, riser inserts, etc. which are used to make a metal casting bypouring molten metal into the casting assembly where it flows to themold assembly and cools to form a metal part.

[0053] Cold-box—mold or core making process which utilizes a vaporouscatalyst to cure the mold or core.

[0054] Downsprue—main feed channel of the casting assembly through whichthe molten metal is poured.

[0055] EXACTCAST® 101/202

[0056] cold-box binder—a two part polyurethane-forming cold-box binderwhere the Part I is a phenolic resin similar to that described in U.S.Pat. No. 3,485,797. The resin is dissolved in a blend of aromatic,ester, and aliphatic solvents, and a silane. Part II is thepolyisocyanate component comprising a polymethylene polyphenylisocyanate, a solvent blend consisting primarily of aromatic solventsand a minor amount of aliphatic solvents, and a benchlife extender. Theweight ratio of Part I to Part II is about 55:45.

[0057] SGT—hollow aluminosilicate microspheres sold by PQ Corporationunder the EXTENDOSPHERE trademark having a particle size of 10-350microns and an alumina content between 28% to 33% by weight based uponthe weight of the microspheres.

[0058] SLG—hollow aluminosilicate microspheres sold by PQ CorporationEXTENDOSPHERE trademark having a particle size of 10-300 microns and analumina content of at least 40% by weight based upon the weight of themicrospheres.

[0059] Gating system—system through which metal is transported from thepouring cup to the mold and/or core assembly. Components of the gatingsystem include the downsprue, runners, choke, etc.

[0060] Mold assembly—an assembly of molds and/or cores made from afoundry aggregate (typically sand) and a foundry binder, which is placedin and/or around a casting assembly to provide a shape for the casting.

[0061] No-bake—mold or core making process which utilizes a liquidcatalyst to cure the mold or core, also known as cold-curing.

[0062] Pouring cup—cavity into which molten metal is poured in order tofill the casting assembly.

[0063] Riser—cavity connected to a mold or casting cavity of the castingassembly which acts as a reservoir for excess molten metal to preventcavities in the casting as it contracts on solidification. Risers may beopen or closed to the atmosphere.

EXAMPLES

[0064] While the invention has been described with reference to apreferred embodiment, those skilled in the art will understand thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims. In this application all units are in the metric system and allamounts and percentages are by weight, unless otherwise expresslyindicated.

Examples 1-2

[0065] Preparation of Disk-Shaped Riser Inserts

[0066] An insulating and exothermic disk-shaped riser inserts wereprepared. The formulation for the insulating disk-shaped riser insertconsisted of a blend of SGT and SLG microspheres, 6% boric acid, and 9%EXACTCAST® 101/201 cold-box binder sold by Ashland Specialty ChemicalCompany, a division of Ashland Inc. The formulation for the exothermicdisk-shaped riser insert consisted of approximately 60% SGTmicrospheres, 9% ISOCURE 101/201 binder, and 31% “thermite” (a mixtureof powdered aluminum, iron oxide, and igniters). The disk-shaped riserinserts were prepared by blowing the formulations into a breaker corepattern with the inserts removed to create disks that were approximately3¼″ in diameter by ⅜″ thick. The pattern was then gassed withtriethylamine in nitrogen at 20 psi according to known methods describedin U.S. Pat. No. 3,409,579. Gas time is 0.5 seconds second, followed bypurging with air at 20 psi for about 15 seconds.

Example 3-4

[0067] Use of the Riser Inserts of Examples 1-2 in a Riser

[0068] The disk-shape riser inserts of Examples 1-2 were dropped into afour-inch open riser with a breaker core, which was part of a“penetration” test casting assembly. FIGS. 2 and 3 show the insulatingand exothermic riser inserts respectively placed in the riser sleevebefore the castings were poured. One of the disk-shaped riser insertswas intentionally placed in the vertical position (see FIG. 2) and theother was place in a horizontal position (see FIG. 3). Molten gray iron,having a temperature of approximately 1480° C. was poured into andaround the test casting assembly.

[0069] Both of the disk-shaped riser inserts floated in the risercavities as the riser cavity filled, so that at the end of the pouring,the disk-shaped inserts were on the top of the liquid metal at the copesurface of the mold. After approximately 20 seconds after pouring, theexothermic disk-shaped riser insert ignited to provide additional heat.

We claim:
 1. A process, for forming a metal casting by pouring moltenmetal into and around a casting assembly comprising an open riser havinga cavity, wherein said process comprises: (a) inserting a riser insertinto the cavity of the riser, and (b) then allowing molten metal to flowinto the cavity of the riser containing the riser insert, wherein, theriser is shaped such that, or contains a barrier such that, the riserinsert does not fall into other parts of the casting assembly before themolten metal is poured, and the density of the riser insert is such thatthe riser insert floats on the surface of the molten metal when themolten metal enters the cavity of the riser.
 2. The process of claim 1where the riser insert acts as a barrier to heat loss from the metal inthe riser by radiation and/or convection to the atmosphere.
 3. Theprocess of claim 2 wherein the riser insert has insulating properties,exothermic properties, or both.
 4. The process of claim 3 wherein theriser is a component of a casting assembly.
 5. The process of claim 4wherein the material used to make the riser insert comprises hollowaluminosilicate microspheres.
 6. The process of claim 6 where the risercontains a physical barrier to keep the riser insert in the riser andprevent the riser insert from falling out.
 7. The process of claim 6wherein the riser contains a breaker core or is a neckdown riser.
 8. Theprocess of claim 7 wherein the riser insert retains insulatingproperties until the metal in riser solidifies.